Is there a way to programatically determine if a font file has a specific Unicode Glyph?

Question

I'm working on a project that generates PDFs that can contain fairly complex math and science formulas. The text is rendered in Times New Roman, which has pretty good Unicode coverage, but not complete. We have a system in place to swap in a more unicode complete font for code points that don't have a glyph in TNR (like most of the "stranger" math symbols,) but I can't seem to find a way to query the *.ttf file to see if a given glyph is present. So far, I've just hard-coded a lookup table of which code points are present, but I'd much prefer an automatic solution.

I'm using VB.Net in a web system under ASP.net, but solutions in any programming language / environment would be appreciated. Thanks!

Edit: The win32 solution looks excellent, but the specific case I'm trying to solve is in an ASP.Net web system. Is there a way to do this without including the windows API dlls into my web site?

Answer 1

FreeType is a library that can read TrueType font files (among others) and can be used to query the font for a specific glyph. However, FreeType is designed for rendering, so using it might cause you to pull in more code than you need for this solution.

Unfortunately, there's not really a clear solution even within the world of OpenType / TrueType fonts; the character-to-glyph mapping has about a dozen different definitions depending on the type of font and what platform it was originally designed for. You might try to look at the cmap table definition in Microsoft's copy of the OpenType spec, but it's not exactly easy reading.

Answer 2

This Microsoft KB article may help: http://support.microsoft.com/kb/241020

It's a bit dated (was originally written for Windows 95), but the general principle may still apply. The sample code is C++, but since it's just calling standard Windows APIs, it'll more than likely work in .NET languages as well with a little elbow grease.

-Edit- It seems that the old 95-era APIs have been obsoleted by a new API Microsoft calls "Uniscribe", which should be able to do what you need it to.

Answer 3

Here's a pass at it using c# and the windows api.

[DllImport("gdi32.dll")]
public static extern uint GetFontUnicodeRanges(IntPtr hdc, IntPtr lpgs);

[DllImport("gdi32.dll")]
public extern static IntPtr SelectObject(IntPtr hDC, IntPtr hObject);

public struct FontRange
{
    public UInt16 Low;
    public UInt16 High;
}

public List<FontRange> GetUnicodeRangesForFont(Font font)
{
    Graphics g = Graphics.FromHwnd(IntPtr.Zero);
    IntPtr hdc = g.GetHdc();
    IntPtr hFont = font.ToHfont();
    IntPtr old = SelectObject(hdc, hFont);
    uint size = GetFontUnicodeRanges(hdc, IntPtr.Zero);
    IntPtr glyphSet = Marshal.AllocHGlobal((int)size);
    GetFontUnicodeRanges(hdc, glyphSet);
    List<FontRange> fontRanges = new List<FontRange>();
    int count = Marshal.ReadInt32(glyphSet, 12);
    for (int i = 0; i < count; i++)
    {
     FontRange range = new FontRange();
     range.Low = (UInt16)Marshal.ReadInt16(glyphSet, 16 + i * 4);
     range.High = (UInt16)(range.Low + Marshal.ReadInt16(glyphSet, 18 + i * 4) - 1);
     fontRanges.Add(range);
    }
    SelectObject(hdc, old);
    Marshal.FreeHGlobal(glyphSet);
    g.ReleaseHdc(hdc);
    g.Dispose();
    return fontRanges;
}

public bool CheckIfCharInFont(char character, Font font)
{
    UInt16 intval = Convert.ToUInt16(character);
    List<FontRange> ranges = GetUnicodeRangesForFont(font);
    bool isCharacterPresent = false;
    foreach (FontRange range in ranges)
    {
     if (intval >= range.Low && intval <= range.High)
     {
      isCharacterPresent = true;
      break;
     }
    }
    return isCharacterPresent;
}

Then, given a char toCheck that you want to check and a Font theFont to test it against...

if (!CheckIfCharInFont(toCheck, theFont) {
    // not present
}

Same code using VB.Net

<DllImport("gdi32.dll")> _
Public Shared Function GetFontUnicodeRanges(ByVal hds As IntPtr, ByVal lpgs As IntPtr) As UInteger
End Function  

<DllImport("gdi32.dll")> _
Public Shared Function SelectObject(ByVal hDc As IntPtr, ByVal hObject As IntPtr) As IntPtr
End Function  

Public Structure FontRange
    Public Low As UInt16
    Public High As UInt16
End Structure  

Public Function GetUnicodeRangesForFont(ByVal font As Font) As List(Of FontRange)
    Dim g As Graphics
    Dim hdc, hFont, old, glyphSet As IntPtr
    Dim size As UInteger
    Dim fontRanges As List(Of FontRange)
    Dim count As Integer

    g = Graphics.FromHwnd(IntPtr.Zero)
    hdc = g.GetHdc()
    hFont = font.ToHfont()
    old = SelectObject(hdc, hFont)
    size = GetFontUnicodeRanges(hdc, IntPtr.Zero)
    glyphSet = Marshal.AllocHGlobal(CInt(size))
    GetFontUnicodeRanges(hdc, glyphSet)
    fontRanges = New List(Of FontRange)
    count = Marshal.ReadInt32(glyphSet, 12)

    For i = 0 To count - 1
     Dim range As FontRange = New FontRange
     range.Low = Marshal.ReadInt16(glyphSet, 16 + (i * 4))
     range.High = range.Low + Marshal.ReadInt16(glyphSet, 18 + (i * 4)) - 1
     fontRanges.Add(range)
    Next

    SelectObject(hdc, old)
    Marshal.FreeHGlobal(glyphSet)
    g.ReleaseHdc(hdc)
    g.Dispose()

    Return fontRanges
End Function  

Public Function CheckIfCharInFont(ByVal character As Char, ByVal font As Font) As Boolean
    Dim intval As UInt16 = Convert.ToUInt16(character)
    Dim ranges As List(Of FontRange) = GetUnicodeRangesForFont(font)
    Dim isCharacterPresent As Boolean = False

    For Each range In ranges
     If intval >= range.Low And intval <= range.High Then
      isCharacterPresent = True
      Exit For
     End If
    Next range
    Return isCharacterPresent
End Function

Answer 4

The code posted by Scott Nichols is great, except for one bug: if the glyph id is greater than Int16.MaxValue, it throws an OverflowException. To fix it, I added the following function:

Protected Function Unsign(ByVal Input As Int16) As UInt16
    If Input > -1 Then
        Return CType(Input, UInt16)
    Else
        Return UInt16.MaxValue - (Not Input)
    End If
End Function

And then changed the main for loop in the function GetUnicodeRangesForFont to look like this:

For i As Integer = 0 To count - 1
    Dim range As FontRange = New FontRange
    range.Low = Unsign(Marshal.ReadInt16(glyphSet, 16 + (i * 4)))
    range.High = range.Low + Unsign(Marshal.ReadInt16(glyphSet, 18 + (i * 4)) - 1)
    fontRanges.Add(range)
Next